"Over six million vehicles are involved in these recalls, which have occurred as far back as 18 months ago and as recently as Monday," it added.

The previous NHTSA warning, issued on 20 October, had covered 4.74 million vehicles.

Vehicle Recalls

On 20 October Toyota ordered the recall of nearly 247,000 Toyota Corolla, Matrix, Sequoia, Tundra and Lexus SC vehicles, sold in the US, to fix defective airbags manufactured by Takata.

Reports said that airbag inflators could malfunction if exposed to consistently high humidity, causing metal fragments to fly out when the bags are deployed in a crash.

In June, Japanese automakers Honda Motor, Nissan Motor and Mazda recalled over two million vehicles to repair potentially faulty airbags and the decision followed a similar move by rival Toyota Motor that month.

Honda's recall covered 2.03 million vehicles, including the Fit compact the world over, the carmaker said in a statement on 23 June.

Nissan's recall covered about 130,000 vehicles, including the Cube.

Mazda recalled 159,807 vehicles worldwide.

On 11 June, Toyota ordered the recall of nearly 650,000 vehicles in Japan to deal with potentially faulty airbags, after Takata warned that further repairs could be needed.

The vehicles covered by the June recall include Corolla and Camry sedans and Tundra trucks.

Takata has, over the last six years, recalled about 16 million vehicles globally for defective airbags. At least four deaths, all in Honda cars, have been linked to the faulty airbags, Reuters reported.